This invention relates to detection of occupant weight in a motor vehicle seat based on the pressure in a fluid filled seat bladder.
Vehicle occupant detection systems are useful in connection with air bags and other pyrotechnically deployed restraints as a means of judging whether, and how forcefully, to deploy the restraint. One fundamental parameter in this regard is the weight of the occupant, as weight may be used as a criteria to distinguish between an adult and an infant or small child.
One prior weight estimation technique is to install an array of variable resistance pressure sensitive elements in the seat, and to sum the individual pressures to determine occupant weight. A restraint system based on this technique is shown and described in the U.S. Pat. No. 5,474,327, issued on Dec. 12, 1995, and assigned to the assignee of the present invention. In practice, however, such systems tend to be relatively costly to implement, and require a significant amount of signal processing for proper calibration and weight estimation.
It has also been suggested to locate one or more fluid or air filled bladders in a vehicle seat, and to estimate the weight of the occupant based on a measure of the pressure in the bladder(s). However, it has been found that such systems can deliver inconsistent weight estimations because both the seat cushion and underlying suspension, which provide a reaction surface for the bladder, tend to be non-uniform in stiffness. Additionally, it is frequently difficult to properly and consistently install the bladders, and to reliably prevent shifting during use.
The present invention is directed to an improved weight estimation apparatus in which an elastomeric bladder is supported on a semi-rigid backer board which is installed in a vehicle seat between the seat cushion and an underlying spring suspension. The bladder is secured to the backer board, and the backer board is attached to the seat, enabling proper and consistent placement of the bladder relative to the seat surface. The backer board provides the reaction surface for the bladder, and masks non-uniformities of the seat structure. Additionally, the backer board will reduce or eliminate the effect of objects lying on the floor under the seat, which might otherwise pinch the bladder and produce weight estimation errors. Further, the board tends to protect the bladder from damage due to sharp objects, pinching by the suspension elements, and the effects of wires or cables routed through the seat. The backer board may be smooth to provide a uniform reaction surface, or contoured to increase or decrease sensitivity to weight applied on certain areas of the seating surface. A bladder port passes through an opening in the center of the backer board and is routed to a pressure sensor. A temperature sensor disposed in proximity to the bladder provides a temperature signal, and a controller estimates the weight of the occupant based on the temperature and pressure signals. Preferably, the pressure sensor is configured to sense the gage pressurexe2x80x94that is, the differential pressure between the fluid and atmospheric pressurexe2x80x94at the center of gravity of the bladder fluid in order to provide a stable output independent of changing atmospheric pressure and changing orientation of the bladder due to vehicle pitch and roll.